Preparation of contact masses



Jan. 6, 1948. H. A. sHABAKf-:R

PREPARATION OF CONTACT MASSES 2 Sheets-Sheet l Filed March 9, 1944 TANKNVENTOR #ausm-A. WBA/ren BZQMM ATTORNEY To l//Prrewr TOR EL EVA JTMH 1l. n NCI TIME /N Hdl/R6 Jan. 6, 1948.

H. A. SHABAKER PREPARATION OF CONTACT MASSES Filed March 9, 1944 loo 15ommm-Arves av "F 2 Sheets-Sheet 2 INVENTOR M A WABAKER amm ATTORNEYPREPARATION F CONTACT MASSES Hubert A. Shabaker, Media, Pa., assignor toBaudry Process Corporation, Wilmington, Del., a corporation of DelawareApplication March 9, 1944, Serial No. 525,666

l 2 Claims.

The present invention relates to the production of contact massesvaluable for use in promoting. entering into, or in any way assistingchemical processes, or as support for catalysts, promoters or otheractive substances which iniluence chemical or other reactions. It dealsin particular with inexpensive and economical processes for treatinginorganic gelatinous substances to produce porous adsorptive catalyticmaterials and also for converting such materials into hard, rigid,strong molded units of predetermined size and shape.

Heretoiore, attempts to produce molded contact masses of high strengthfrom synthetic materials. for example, sels. selatinous precipitates andthe like, have met with limited commercial success. Gels or gelatinousprecipitates are, because o! their gelatinous or jelly-like texture,lllsuited for economical treatment or handling to produce adsorptivecatalytic materials and due to their tendency to shrink greatly ondrying they are not adapted to commercially feasible continuousprocesses for producing strong molded units. After they have beenconverted to dry, hardened and preferably granulated, comminuted oriinely divided form, they are easily and cheaply purified, but in thiscondition they have little or no plasticity and it is necessary in orderto make them suitable for simple molding operations to add a plasticmaterial or other binding agent. In many instances, use of binding orplasticizing agents so modifies the porosity, activity, reactivity orother desired properties oi' the material as to reduce its value as acatalyst. When it has been necessary or desirable to utilize little orno binder, molding methods involving stamping. extreme pressure, and/orimpact have been utilized, but such methods are costly. Moreover, hard,abrasive materials of the nature ot dry vitreous gels tend to causeexcessive wear in machines designed to effect this type of molding.

One object of the invention is to provide methods for producingcontinuously contact material suitable for commercial use from solutionso! starting materials or reactants. Another object is to produce fromgels or gel-like substances solid contact material having stability ofactivity. Another object is directed to the economical and eilicientprocessing of wet gels or gelatinous precipitates to produce porous,stable bodies of contact material on a commercial scale. Another objectis directed to an economical process for effecting rapid and eilicientremoval of water and impurities from a gel or gel-like material. Otherobjects will become apparent from the detailed description 'whichfollows.

The invention involves a particular sequence of steps for treating a gelor gel-like substance which is produced by interacting a plurality ofreactants, for example, aqueous solutions capable of producing inorganicgels or gelatinous precipitates containing one or more oxides orhydroxides. The gel or gel-like substance is produced under conditionsor 'is maintained or treated under conditions directly after itsproduction in order to permit the substance to be dried economically andrapidly so that the substance attains the physical state which isnecessary to place it in condition for further processing. Thisinvention has special application to plural oxide catalysts of thesiiiclous type.

The conditions under which the gel substance is formed or under which itis maintained after its formation, in addition to providing for rapidand economical drying, also lowers the gravity of the final product,provides a catalyst having stability of activity as indicated by itsability to resist loss of activity on contact with steam at elevatedtemperatures and gives to the material the necessary characteristics forproducing readily molded or cast products which are highly porous andhave the necessary strength and hardness to withstand long periods ofcommercial use. Due to the preliminary treatment of the gels the dryingcan be effected under fairly moderate temperature conditions and for arelatively short period of time to produce a irlable or flaky material.The material in this physical state permits a rapid and effectiveremoval of impurities therefrom which would adversely affect theactivity or the molding characteristics of the ilnal product. Afterremoval of impurities from the material it is then further treated in amanner to change it to such a plastic state that it is readilydeliverable t0 molds and formed into rigid products which are furthertreated for the purpose of adjusting the activity and increasing thehardness of the products,

In the drawings, Fig. 1 is a flow sheet of a commercial plant in whichthe indicated operations are arranged in four stages, and Fig. 2 is agraph of aging conditions in accord with this invention.

Referring to Fig. l of the drawings, the mixing device I0 wherein thegel is formed receives streams of reactant solutions for forming the gelfrom lines Il and I2. The mixer l0 may be a single or multiple stagereactor and will preferably take the form of any of those disclosed inmy copending application Serial No; 398,731, iiled June 19, 1941, now U.S. Patent No. 2,370,200, issued February 22, 1945 for Production ofsolids from reactant solutions, or of the type disclosed in Patent No.2,232,727, issued to A. G. Perkin and myself February 25, 1941. Thesereactors are designed to provide a conned chamber with the inlets for.the reactant solutions communicating therewith in a manner to provideconditions of great turbulence within the chamber so that the gelformation is substantially instantaneous within the chamber. Thereactant solutions are fed to the mixing device l continuously and theformed gel is continuously removed therefrom and fed to a conveyor I3through which the gel is removed from the reaction zone to thereactivation zone and distributed on a dryer generally indicated 'at i4,wherein the second or activation stage of the process is begun. In orderto increase the surface area of the gel so that greater surface issubjected to the drying medium, the gel is subdivided prior to beingdelivered to the dryer I4 by any suitable means.

A substantial portion of the water content of the gel is removed beforeit reaches the drier M by arranging conveyor belt I 3 to inclineupwardly to permit water to drain therefrom. Provision is made to agethe gel before it reaches the drier in order that the .final product hasactivity stability as well as physical stability. The aging may beaccomplished in several ways and preferably is done while the geltravels up the belt lI3 to the drier and for a period preferablysumciently long for syneresis to occur so that the syneresis water candrain from the belt into a sump l5 from which it can be removed throughline I6. The conditions under which the aging is carried out are suchthat there is substantially no Water removal by evaporation. Only thewater of syneresis is removed during this step, which permits the dryingstep, wherein a substantial portion of the water remaining in the gel isremoved by evaporation, to be effected rapidly and economically. Asmentioned above, the aging of the gel may be carried out in variousways, such for example, as disclosed in the copending application of J.R. Bates and myself, Serial No. 427,918, filed January 23, 1942 (issuedDecember 24, 1946 as U. S. Patent No. 2,412,958), wherein the gelundergoes a fast aging step in which it is subjected to a mixture ofsteam and air at about 175 F. for approximately one-half hour. Or thegel may be rapidly aged in various other ways, for example, by immersionin a hot liquid such as water or oil maintained between 150 and 250 F.for about two hours or less, or the reactant solutions may be deliveredto the mixing device at elevated temperatures, for example, around 160F. and the gel maintained at about that temperature after its formationuntil it is delivered to the drier. Products of good activity, stabilityand physical characteristics have also been obtained by slow aging thegel at low temperatures, such as room temperature, for extended periodsof time, from 24 to 48 hours.

Fig. 2 discloses aging conditions in accord with the present invention.The aging is eiected at a temperature above 70 F. and for a time of atleast 5 minutes. The time and temperature of aging are correlated to lieabove and to the right of the line AB in this ligure. For deinitenesswith respect to the position of the-line AB it is noted that it passesthrough 025 hour at 160 F. and is at 0.083 hour (5 minutes) at 210 F.When produced under these conditions catalytic gels are obtained bydrying and purifying of soluble materials, the catalytic properties ofwhich are relatively stable with respect to materials which are not soaged. When the gels are formed into agglomerated pellets the pellets arerelatively extremely hard in comparison to pellets not so aged.

After the gel has been aged and the syneresis water drained therefrom,it is delivered to the drier I4 where, due to the removal of thesyneresis water during the aging, it may then be dried rapidly even atmoderate or low temperatures, for

example, below 500 F. In practice it has been found that eilicientdrying is had when the gel is subjected to low temperatures between to200 F. at the beginning of the drying zone and then subjected toprogressively increasing temperatures until at the end of the dryingzone the material is dried at between 250 and 400 F.

As the gel substance passes through the drier I 4 a large amount ofwater is evaporated therefrom, for example, about 10 lbs. of water wouldbe evaporated to produce 1 lb. of nal product.

When the material reaches the end of the drier I4 it is in a friable orflaky stateand sufficient water has been removed therefrom to preventthe material in this condition from going into solution or reverting tothe gel state upon the addition of water in the further treatment of thematerial.

In the dried condition any impurities may readily be removed from thegel by water washing or chemical treatment and it is essential that thestep of removing impurities be conducted prior to delivering thematerial to the activity adjusting zone. The degree of flneness of thematerial as it leaves the drier M will determine the particularoperating conditions for removing the impurities therefrom. It has beenfound in practice that generally the best procedure is to pulverize thematerial before treating it to remove impurities. To this end, thematerial from drier I4 is discharged into hopper I1 for delivery intosuitable granulating or pulverizing equipment indicated at I8, fromwhich it is removed in pulverized condition to a second hopper i9 priorto undergoing the impurity removing treatment. The impurity removingoperation may comprise various forms of apparatus elements andpreferably the elements will be arranged so that a continuous washing orchemical treating operation is effected. As indicated, the pulverizedsubstance will be directed from hopper I9 to one or more treatingvessels 20 and 20a, which may be arranged in cascade, and therein thepulverized material is contacted with a selected treating agent whichissupplied by line 2|, rst to vessel 20a. The partially spent treatingagent is conducted from vessel 20a to vessel 20 by line Zia, and thespent agent after contact with untreated gel in the last named vessel isdischarged from the system by line 2lb. The gel material in the treatingvessels 2II and 20a is a slurry and may be treated with chemicals, suchas acids, alkalis or salts, or washed with water or .with anycombination of these. It is then pumped to vessel 22 where it isadvantageous to wash the treated substance with a pure wash water, suchas distilled water, which' may be supplied to vessel 22 by line 23. Theused wash water, removed from vessel 22 through line 23a, is dischargedfrom the system through line 23h. If desired, the used wash water fromvessel 22 may be conducted from line 23a through line 23e to line 2| andused as an ingredient for treating the substance in treating vessels 20and 20a. l

After the material has been treated or washed and suiicient impuritiesremoved therefrom it is necessary that the treating or washing liquids,or a portion thereof, be removed from the material in order to place thematerial in a physical state which is suitable for commercial use. Thematerial from the washing Stage is then directed to filters 24 where,after suflicient liquid is removed therefrom, the iinely dividedfiltered material may be removed from the filters and used as acatalytic material, or it may be sent to driers 25 for further waterremoval if necessary. The driei's 25 may, as indicated, be provided withsuitable dust collectors and the collected particles returned to asuitable point in the system, such as hopper I3.

It is at times advantageous if the substance leaving the drier Il isground or pulverized prior to the washing step, since for someunexplainable reason the filtering characteristics of the material aregreatly increased. For example, if the material is treated directly fromthe drier to remove impurities the cake formed during the filtering stepis exceedingly thin, as of the order of in thickness, while if it ispulverized or granulated directly from the drier and then treated toremove impurities, the filter cake attains a thickness upwardly of 2"which is a considerable advantage in large commercial operations.

As heretofore mentioned, the material, after iiltering or dryingoperations, is then in condition for use as a contact material orcatalyst, since it is then in the pure state, or contains only anegligible amount of components which would be deleterious to chemicalprocesses and the various treatments following the gel formation,particularly the aging step, has given to the material stability of itscatalytic activity. The various treatments which the gel has undergoneafter its formation have additionally given to the material othercharacteristics, for example, the ability of the particles of thematerial to adhere to each other resulting in physical strength inmolded agglomerates. After leaving the activation zone the material isin excellent condition for molding into units of desired size and shapeand the material may be directed by conveyor 26 to hopper 2l in themolding zone from which it is delivered to a pulverizer 23 where it isground or subdivided to a degree of neness of 100 to 200 mesh in orderto condition it to be placed in a somewhat plastic state by furthertreatment so as to provide a readily moldable substance. From thepulverizer 28 the material is led to a mulling or kneading zone 3lthrough a feed hopper 29. A controlled amount of water or other liquidis added to the material in zone 30 through line 3|, for example, andthe gel is subjected to vigorous mechanical treatment in order tothoroughly work the liquid into the dried gel particles and develop aheterogeneous paste.

The material leaving the activation zone may be formed into a paste invarious ways, for example, the liquid may be supplied directly from anysource through line 3l, or the liquid may comprise the spent washmaterial from the activation zone. An efficient commercial operation hasbeen conducted by drying or filtering only a portion of the washedmaterial in the activation zone and adding to this dried portion anotherportion of material directly from the washing stage sutilcient in amountto give desired plasticity to the material in the mulling zone'll.

The quantity of liquid utilized is regulated to produce a substantiallyconstant composition of moldable consistency though the quantityrequired will vary between wide limits, depending upon the physicalcharacteristics of the material leaving the activation zone. Generallythe quantity of wetting material required will be within the range of 30to 150% by weight of the filtered gel in order to provide a paste havinga consistency capable of being flowed into casting molds. As disclosedin my Patent No. 2,299,768, issued October 27, 1942, the mulling orkneading treatment in zone 30 may be such as to provide a heterogeneouspaste which sets to solid form upon standing and reverts to moldableconsistency upon being agitated.

One molding operation particularly well adapted for continuousproduction of large quantities of molded product is one in which themold.. able material is flowed into casting dies or molds, converted tohard form in the dies and ejected or otherwise remove from the dies inthat condition. As shown diagrammatically in the pelleting machineindicated generally at 32 the casting dies or molds are preferablyarranged in a continuous belt 33 which travels first through a loadingzone containing a suitable device 34 for receiving moldable mixture fromkneader or muller 30 and applying it to the molds, then through ahardening or setting zone wherein the cast material is allowed to set orharden or is treated to effect this result, and then through anunloading zone containing suitable means, indicated at 35, arranged andadapted to remove the hardened material from the molds as by pushing orpunching action, by blowing with jets of air and/or by vibration of belt33. The hardening of the molded material, especially if it be a,thixotropic mixture, may consist in allowing suilicient time for it toset to hard form. In most cases, a better product is obtained when themolded units are dried by passage once or any desired number of timesthrough a heated hardening zone whose temperature may be maintained at alevel similar to or higher than that employed in dryer i4, by suitableheating elements, for example, pipe coils heated by steam. If desired,the molded units or pellets after ejection from belt 33, may besubjected to further hardening in the heating zone as by passage throughthat zone on conveyor belt 36, as shown.

'I'he molds in belt 33 are preferably treated to remove adherentparticles of gel and the like and/or to lubricate the walls of thecasting cups or perforations, before their return to loading position.To this end, they may be subjected to treatment with a. solution ofalkali, acid or salt or other material capable of dissolving theadherent solid supplied by line 31 and spray nozzles 31a, followed bywashing with water and/or a lubricant supplied by line 38 and sprays38a. I'he molds may have excess liquor removed therefrom after either orboth washing steps, for example, by heating or drying or by use of a.vacuum jet, such as indicated digrammatically at 39.

The fourth stage of the process as indicated involves treatment of themolded product to adjust its adsorptive capacity or catalytic orchemical activity and to improve its value for its intended use, forexample, to improve its ability to assist desired reaction and/or toreduce its tendency to produce formation of by-products. The adjustmentmay involve chemical or physical treatment of the mass at controlledtemperature with active or inert fluids for the purpose of activating,deactivating, modifying or removing certain components thereof, as forexample, by reduction or oxidation, or by treatment with inert orchemically active fluids which selectively control or modify activity ofany or all of the components or constituents of the molded products.

` sacaste One type of treatment valuable for controlling 'the activityof many contact masses having a plied by line 43 heated to desiredtemperature in coil heater 44 and flowed by line 45 to treater 4I. Oneadvantageous gas treatment of plural component contact masses comprisingor containing one or more oxides from the group silica, alumina,zirconia, berylliarfor example, and intended for use in the treatmentor-trawrmation of hydrocarbons and their derivatives. is, as disclosed inthe copending application of John R. Bates, Serial No. 289,915, filedAugust 12, 1939, now abandoned,

to subject the molded material to an atmosphere containing up to 100% ofsteam at controlled temperature within or above the range of 600 t 1600F., as for example at 800 to 1400 F. for suitable periods of time up toseveral hours.-

The discharge of molded material from treater 4I, after cooling incooler 40, is screened by sieve 41 to remove the small quantity of finesthat may have accumulated in the molding, drying and activity adjustmentsteps. The finished pellets of desired size fall into hopper 48 fromwhich they may be removed as required or desired for bag ging or otherpacking for shipment. The nes passing through the screen may be returnedto an intermediate stage of the process for reworking, in which eventthey may be added by line 49 to the pulverized material flowing into themolding zone, or may be led by lines 49 and 50 to the nely divided gelentering the treating or washing stages in the activation zone. Ifdesired, sieve 41 may be supplemented or replaced by a sieve disposedbefore the gas treater, the lines from which may be reworked asdescribed in connection with sieve 41.

The purified material from the filters 24 or dryers 25 may be treateddirectly in the activity adjusting zone without undergoing treatment inthe molding zone since, as heretofore pointed out, the material leavesthe activation zone in condition for immediate use ior some contactingoperations. The apparatus heretofore described in connection with theactivity adjusting zone, although adapted for molded or pelletedmaterial, can readily be adapted for handling the line granular materialfrom the activation zone in order J to provide the proper activityadjustment.

When steam is used as a heating medium for conducting drying processes,for example in dryer I4 and/or in pelleting machine 32, the condensedwater produced in the drying coils may be utilized as a source ofpuriiied water for assisting in one or more of the steps of processingor making a gel. To this end, the condensate may be collected in asuitable tank I from which it may be withdrawn by line 52 as desired orrequired and forced through line 53 into line 38 for use in washing thecasting molds and/or through line 54 to either or both lines 23 and 2ifor use in the treating solution utilized in treating zones and 20a.Suitable quantities of the condensate may be utilized in the preparationof the reactant solution fed to lines I I and l2. Any excess condensatemay be conducted through line 55 to be utilized as a cooling medium incooler 4l.

Hardening of the molded units is eiIected by passage of the belt 33through a heated zone maintained at temperatures sufficiently high todrive oit part or all of the moisture and harden the molded units. It ispreferred to employ low or moderate temperatures for this step, as forexample, up to 500 F. However, any desired temperature below the fusionpoint of the molded mass, for example, up to 1600 F., as within therange of 900 F. to 1400 F., may be utilized, especially in instanceswhere high temperature does not impair the product or interfere with anysubsequent treatment.

One typical application of the invention is in the production of moldedcatalysts of predetermined activity consisting essentially of silica andalumina. A gel was continuously prepared in the reaction zone in amixer, having a cylindrical reaction chamber and discharge nozzle ofabout 21/2 inches in diameter and a length of about 4% inches, bycoagulating a stream of silica-alumina sol with a stream of a solutionof a salt containing a volatile cation after the manner disclosed inPatentNg. 2,283,173, issued to John R. Bates, May 19, 1942. The sol wasmade by feeding to the mixer-'at pressure above 10 lbs/sq. in. gauge,122 volumes of sodium silicate solution and about 170 volumes of sodiumaluminate solution, the sodium silicate beingl made by diluting about105 parts by weight of a commercial sodium silicate containing about28.8% silica with about` parts by weight of water, and the aluminatesolution by dissolving about 27 parts by weight of solid commercialsodium alumlnate of about 55% alumina content in about 1'10 parts byweight of water. About 97 volumes of ammonium sulphate solution, made bydissolving approximately 27 parts by weight 'of solid ammonium sulphatein about 83 parts by weight of water, was injected in the form ofseveral high velocity jets into the stream of silica. alumina soltraversing the reaction chamber. The rapidly gelling mixture wasimmediately violently agitated for about 0.1 second by a rapidlyrotating mixing blade and the resulting completely formed zeolitic gelwhich had a pH of about 9.6 and which contained about 9% by weight ofwater insoluble oxides owed from the mixer as a stiil, continuous bodywhich contained or embraced all the constituents of the streams ofsodium silicate, sodium alumlnate and ammonium sulphate solutions. Therate of ilow of these streams into and through the reaction chamber wassuch that only about 0.4 second elapsed between the mixing of the soland ammonium sulphate Solution and the ejection of the all embracing gelfrom the mixing head. At intervals of about one to three hours, the iiowwas transferred from one mixer to another for the purpose of removingaccumulated gel. f

The stream of gel was continuously collected on an inclined conveyer onwhich the process of aging was allowed to proceed while the gel wassimultaneously heated to about 150 F. The conveyer discharged thematerial through a 3 mesh screen granulator on to a continuous drier inthe activation zone operated at about 200 F. 'I'he resulting hard,vitreous zeolitic solid was ground to mesh size and ner and was thensubjected to continuous counter-current washing and base exchangetreatment with a solution of ammonium chloride until an ammonium zeolitecontaining less than about 0.5% by weight of sodium oxide was produced.

casacca After water washing, filtering and drying, the ammonium zeolitewas mixed with an approximately equal weight of water and subjected tovigorous kneading and mulling action for about 30 minutes in the moldingzone. The heterogeneous and comparatively thin thixotropic paste soproduced was formed into a continuous sheet which was flowed without theuse oi' substantial pressure into perforations of about 4.5 mm. dlameterextending entirely through continuously moving casting plates of about 4mm. thickness which formed the molding belt. Then the cast material wasdried in the moving plates at temperatures of about 300 F. whereupon thehardened pellets were ejected from the plates and were then treated forabout hours while being maintained above 1000 F. with a moving stream ofsteam.

From the above described quantities of reactant solutions fed to themixer the plant continuously produced the finished pellets at the rateof about 60,000,000 per day. These pellets were capable of uniformlywithstanding concentrated loads in excess of 1,000 grams applied acrosstheir axes through a knife edge oi' the type commonly used foranalytical balances, and consisting of the substantially puresilica-alumina nucleus of the aeolite. They were highly adsorptive andwere valuable for use in contact processes involving selectiveadsorption oi' fluids. for example, to separate desired gases fromgaseous mixtures or as a ltering or decolorlzing medium for removingunstable and color bodies from syrups or oils. Also they were valuablefor catalyst or catalyst support for promoting decomposltions includingdehydrogenation and splitting reactions and for promoting synthesisincluding reactions involving polymerization, alkylation andcondensation reactions. Also, these silica-alumina pellets were valuablefor use to effect, promote, or as support for metals or oxides whichpromote or effect desulphurization and other purification of hydrocarbongases and liquids, coke oven gas and the like. When used in processesinvolving periodic regeneration to remove carbonaceous, sulphur-ous orother deposit by combustion or extraction they were capable of retainingtheir size and shape, catalytic activity and/or adsorptive capacity forprolonged periods of use in which they were subiected to repeated andfrequent regeneration.

Following is a chart showing various conditions oi' treating a gel andthe characteristics of the product obtained. In the production of thecatalyst the gel was aged as disclosed in the specification in order toprovide for fast and economical drying.

Aging Cmditions. Stability Appar- Hard- Activity ent nem. Per Cent ActivHm Temp., Density Grams Gaso. Hard- Per Cet F. ness Gaso the pellet, wastaken as the measure of hardness. The activity of the three catalystswas adjusted prior to the activity measurement by treating ior 10 hoursat i400 F. in a mixture of 5 mol percent steam and mol percent air. Thecatalysts were tested for steam stability with respect to hardness andactivity by treating them for four hours at l350 F. in 100% steam. Theactivity of the catalyst initially and after steam aging was determinedby measuring the percent by volume of the gasoline based on initialcharge stock produced during cracking run in which a light East Texasgas oil was charged to the catalyst at atmospheric pressure, thecatalyst being maintained at 800 F. at a rate of 11/2 liquid volumes ofgas oil per volume of catalyst per hour for a ten minute period.

When a gel produced by the above described typical method had not beenaged but was dried and treated to adjust activity under the conditionsoi the typical method it was noted that the apparent density was high,of the order of .7. The hardness was extremely low, of the order of 400grams, and the activity stability was low, of the order of about 20%.

Similar improvements are obtained by the present process with othercontact masses, as for example, with catalysts containing a majorproportion of silica and minor proportions of alumina, zirconia andberyllia. Also improved catalysts are obtained by this processcontaining silica and any one or two of the materials alumina, zirconiaand beryllia.

Although the invention has been described in connection with one typicaloperation, it is to be understood as exemplary only and not limitativeof the invention which is to be limited only by the appended claims.

The present application is a continuation-inpart of application SerialNo. 349,794, iiled August 2, 1940, now abandoned.

I claim as my invention:

1. 'I'he method of producing a catalyst in the form of hard, low-densitypellets highly stable to deactivation by steam, which comprisespreparing a plural inorganic hydrogel comprising a hydrous oxide ofsilica., said hydrogel containing alkali metal salts as an impurity,aging said hydrogel in freshly prepared state without intermediatetreatment following its preparation and at a temperature of at least '70F. and for a time of at least 5 minutes, the temperature and time beingcorrelated to lie above and to the right of the line AB in theaccompanying drawing, rapidly drying the aged hydrogel, pulverlzing thethus obtained dried gel, washing and treating the pulverized gel toremove alkali metal salts, iiltering the washed gel then again dryingthe same, forming the dried gel into paste with the addition of water,casting the paste into pellets, drying and calcining the pellets.

2. The method oi' producing silica-alumina catalyst in the form of hard,low-density pellets highly stable to deactivation by steam, whichcomprises preparing a hydrogel comprising hy drous oxides of silica andalumina, said hydrogel containing alkali metal salt as an impurity,aging said hydrogel in freshly prepared state without intermediatetreatment following its preparation and at a temperature of at least 70F and for a time of at least 5 minutes, the temperature and time beingcorrelated to lie above and to the right of the line AB in theaccompanying drawing, rapidly drying the aged hydrogel, pulverizing the11 thus obtained dried gel, wsshingnd treating the pulverized gel toremove alkali metal salts, i'lltering the'washed gel then again dryingthe same, forming the dried gel in to paste with thev addition ot water.casting the paste into pellets, drying and calcining the pellets.

HUBERT ASHABAKER.

REFERENCES CITED The lfollowing references are of record in the V me ofthis patent:

Number UNITED STATES PATENTS Name v Date Holmes June 10, 1930 Miller'--Aug. 5, 1930 Weil -1-- Jan. 10, 1933 Brown Apr. 16, 1935 Bein-man May18, 1926 Y Bond Feb. 14, 1939 Connolly et ai. 7.--- Aug. 10, 1943Shabaker Oct. 27, 1942 Connolly Feb. 8, 1944 Stewart 7- July 13, 1926

